A number of coral species survive at seawater temperatures far higher than estimates for the tropics during the next century.

We associate coral reefs with tropical seas of around 28 degrees so in that mindset even slight warming can have devastating effects on corals. But in the Arabian/Persian Gulf, corals survive seawater temperatures of up to 36 degrees Celsius every summer, heat levels that would kill corals elsewhere. Corals have adapted.

Reefs are made up of many species of coral, each of which have a mutually beneficial, or “symbiotic”, relationship with algae living in their tissue. These algae supply vital nutrition to the host but are sensitive to environmental changes including increases in seawater temperature. [...]In Gulf corals, both the coral host and the associated algal partners need to withstand the high seawater temperatures,’ said Dr Wiedenmann who led the study.

But the scientists were surprised to discover that the algae in Gulf corals belong to a group not known for its thermal tolerance.

‘We see that the algae are indeed special but in a way that we did not expect,’ said Dr Wiedenmann. ‘The algae that we found in most of the corals in Abu Dhabi reefs were previously described as a ‘generalist strain’ that is usually not found in corals exposed to high levels of heat stress.’